1. Field of the Invention
This invention relates to an epoxy resin composition. The invention also relates to a method of preparing an epoxy resin composition.
2. Description of the Relevant Art
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical properties. The resins are characterized by epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties.
The most common epoxy resins are a condensation product of epichlorohydrin and bisphenol A. These resins can be cured with conventional curing agents such as polyamines, polycarboxylic acids, anhydrides and Lewis acids. Bisphenol A based epoxy compositions when cured have good adhesive properties but many are inherently stiff and brittle and hence their use is limited to applications where peel forces are not significant.
It has been found that plasticizers can be added to an epoxy resin adhesive system to improve flexural strength. Typical methods of plasticization include the addition of flexibilizing aliphatic amines to the curing agent, addition of aminated or carboxylated rubbers to the system, addition of carboxy-terminated polyesters, addition of organic hydroxyl containing compounds and the addition of epoxidized oils.
A process for preparing polyoxyalkylene polyamines is described in U.S. Pat. No. 3,654,370 to Yeakey. This patent describes curing agents for epoxy resins of the formula ##STR1## wherein R is the nucleus of an oxyalkylation susceptible polyhydric alcohol containing 2 to 12 carbon atoms and 2 to 8 hydroxyl groups, Z is an alkyl group containing 1-18 carbon atoms, X and Y are hydrogen or Z, n has an average value of 0 to 50 and m is an integer of 2 to 8 corresponding to the number of hydroxyl groups in the polyhydric alcohol. These amines are synthesized by means of a nickel, copper and chromium amination catalyst.
U.S. Pat. No. 3,236,895 to J. M. Lee and J. C. Winfrey and U.S. Pat. No. 3,462,393 to Legler are pioneer patents. They describe a series of amine compounds which are solids or liquids and have utility particularly in curing epoxy resins. The amine compounds have the general formula: ##STR2## wherein Rs are selectively defined as hydrogen, alkyl radicals and alkylene oxide radicals and x and m are defined integers.
U.S. Pat. No. 4,316,991 to G. P. Speranza et al discloses modified polyols for use in preparing flexible urethane foams. A polyol initiator is reacted with one or more alkylene oxides and an epoxy resin in such a manner that the epoxy resin is added internally along the length of the polyol chain. The result is a modified polyol having a molecular weight in the range of 2,000 to 7,000. U.S. Pat. No. 4,373,034 to G. P. Speranza et al discloses the reaction of these modified polyols with polyisocyanate and a foam catalyst in the presence of a blowing agent to yield a flexible polyurethane foam.
U.S. Pat. No. 3,299,169 to J. C. Smith discloses an elastomeric epoxy resin. Epoxy resins are cured with a polyoxyalkyleneamine to yield these compositions.